Passage Of Beam Research Articles

A Wavefront Division Polarimeter for the Measurements of Solute Concentrations in Solutions.

Polarimeters are useful instruments that measure concentrations of optically active substances in a given solution. The conventional polarimetric principle consists of measuring the rotation angle of linearly polarized light. Here, we present a novel polarimeter based on the study of interference patterns. A Mach–Zehnder interferometer with linearly polarized light at the input is used. One beam passes through the liquid sample and the other is a reference beam. As the linearly polarized sample beam propagates through the optically active solution the vibration plane of the electric field will rotate. As a result, the visibility of the interference pattern at the interferometer output will decrease. Fringe contrast will be maximum when both beams present a polarization perpendicular to the plane of incidence. However, minimum visibility is obtained when, after propagation through the sample the polarization of the sample beam is oriented parallel to the plane of incidence. By using different solute concentrations, a calibration plot is obtained showing the behavior of visibility.

Spectral and spatial shaping of Smith-Purcell radiation

The Smith Purcell effect, observed when an electron beam passes in the vicinity of a periodic structure, is a promising platform for the generation of electromagnetic radiation in previously-unreachable spectral ranges. However, most of the studies of this radiation were performed on simple periodic gratings, whose radiation spectrum exhibits a single peak and its higher harmonics predicted by a well-established dispersion relation. Here, we propose a method to shape the spatial and spectral far-field distribution of the radiation using complex periodic and aperiodic gratings. We show, theoretically and experimentally, that engineering multiple peak spectra with controlled widths located at desired wavelengths is achievable using Smith-Purcell radiation. Our method opens the way to free-electron driven sources with tailored angular and spectral response, and gives rise to focusing functionality for spectral ranges where lenses are unavailable or inefficient.

Thomson scattering upgrade in RFX-mod: alternative designs for injection and collection optics

RFX-mod RFP is now under shutdown and it is undergoing a deep modification in the plasma magnetic boundary, with changes in the vacuum vessel, first wall and stabilizing shell. A diagnostics upgrade is also foreseen; in particular, an improvement in the signal level of the main Thomson Scattering Diagnostics becomes crucial for the diagnostic operation in low density RFP and tokamak discharges. Launching and reflecting optics for a double passage of the laser beam in the equatorial plane is needed, as well as a manipulator for retroreflector substitution and precise positioning. Analysis of the expected energy density on the optics is presented; stray light generation, positioning issues and optical damage risk are examined. Moreover, beam retro-reflection allows in principle re-injection in the edge Thomson Scattering system, lying at another toroidal position; this possibility is analyzed focusing on the reflected beam profile and pointing stability. Alone, laser beam recirculation can provide a doubling in the signal level, while a further 30% gain can be obtained maximizing the collection optics transmission: an alternative, simplified design featuring a 3 elements objective is presented and discussed, the major drawback being a non-planar image surface.

Progress of Thomson scattering diagnostic on HL-2A tokamak

Some efforts have been made to promote the performance of incoherent Thomson scattering (TS) diagnostic on HL-2A tokamak. Motorized stages are used to adjust the reflecting mirrors and focusing lens of the input laser beam optics, by which it is easy to control the laser beam pass through the narrow throats of the lower and upper closed divertors. Spectral calibration has been refined. Hardware of Si-APD detector electronics is improved, which provides two output signal channels. In one channel, only the rapid TS signal is output after deducting the influence of plasma light. In the other, both the rapid TS signal and the background signal of slow-varying plasma light are output. In this 2017 experiment campaign, the new developed electronics are tested and TS signals can be obtained from the two channels, which are digitized by 1GS-12bit transient recorders. In data processing, the TS pulse shape is fitted with different functions output from the two different channels. The statistical estimation of Te data is also optimized. More channels of high-speed digitizers and more positions of Te and ne measurement are planned and are in constructions.

Femtosecond Laser-Inscripted Direct Ultrafast Fabrication of a DNA Distributor Using Microfluidics

A femtosecond laser can be used for single or multiple writing processes to create sub 10-μm lines or holes directly without the use of masks. In this study, we characterized the depth and width of micro-channels created by femtosecond laser micro-scribing in polydimethylsiloxane (PDMS) under various energy doses (1%, 5%, 10%, 15% and 20%) and laser beam passes (5, 10 and 15). Based on a microfluidic simulation in a bio-application, a DNA distributor was designed and fabricated based on an energy dose of 5% and a laser beam pass of 5. The simulated depth and width of the micro-channels was 3.58 and 5.27 μm, respectively. The depth and width of the micro-channels were linearly proportional to the energy dose and the number of laser beam passes. In a DNA distribution experiment, a brighter fluorescent intensity for YOYO-1 Iodide with DNA was observed in the middle channels with longer DNA. In addition, the velocity was the lowest as estimated in the computational simulation. The polymer processability of the femtosecond laser and the bio-applicability of the DNA distributor were successfully confirmed. Therefore, a promising technique for the maskless fabrication of sub 10-μm bio-microfluidic channels was demonstrated.

Acoustic beam anomalies in automated breast imaging.

In B-mode imaging of the dependent or compressed breast, wave incidence at steep angles can change propagation directions and induce areas of signal dropout. To evaluate the image anomalies in reasonable simulation times, we performed full-wave studies for center frequencies of 1 and 4MHz. Speed of sound and density of skin, typical coupling gel, and adipose tissue were assigned to the test couplant. Compared with commercial gel, skin-like couplant reduced the dropout area at 1 and 4MHz by 57.1% and 96.7%, respectively, consistent with a decreased average beam deflection in the breast. Conversely, the adipose-like couplant increased the dropout area from that of simulated commercial gel by 26.5% and 36.7% at 1 and 4MHz, respectively. In addition, the skin-like couplant resulted in the greatest beam deflection inside the breast among all couplants. The findings could aid the use of three-dimensional simulations to design ultrasound couplants for beam passage through tissue boundaries at steep angles to improve corrections of signal dropout and defocusing and in compound imaging.

Abstract ID: 223 The promise of the MRI linac: Simultaneous MRI and irradiation

Introduction Image guidance during radiotherapy is widely applied in the current clinic. Prior to treatment a variety of imaging modalities is used to localize and characterize the tumour and the surrounding organs at risk. These data are used to optimize the treatment plan, i.e. optimize the radiation dose delivery. Still, during the course of radiotherapy many sources of geometrical uncertainties exist, leading to treatment margins and with that to unwanted involvement of healthy tissues in the targetted volume. By integrating 1.5 T MRI functionality with a radiotherapy linear accelerator (linac), the anatomy can be visualized during irradiation and thus decreasing the geometrical uncertainties and improve the targetting. Materials and methods Together with Elekta (Stockholm, Sweden) and Philips (Best, The Netherlands) a 1.5 T MRI system is integrated with a 7.2 MV linac. The active shielding of the MRI as well as the layout of the linac is modified to mitigate the magnetic interference. A dedicated cage of Faraday was designed to mitigate the RF interference and a beam window in the MRI was created to allow beam passage. In parallel with the hardware developments a pipeline for daily online and ultimately real-time plan adaptation has been set-up. This enables to adapt the plan as soon as an anatomical change is detected. The pipeline can re-optimize the treatment plan for the latest state of the anatomy while taken into account the dose delivered so far. This loop can be run daily but also on an intra-fraction time scale. A major deviation from conventional systems is that the dose is delivered in the presence of a magnetic field. This affects the dose distribution but also affects dosimeters. The impact of the magnetic field can be investigated and subsequently accounted for by Monte Carlo simulations. By doing so, we can quantify the impact on dose and dosimeters. Results and discussion The first prototype MRI linac gave the proof of concept for simultaneous irradiation and MRI. The second prototype showed MRI guided IMRT. The third prototype in Utrecht is the pre-production MR linac and currently the fourth MR linac is installed, this is the pre-clinical MR linac that will be introduced in the clinic. Currently the system is being accepted and commissioned for clinical introduction. The adaptive treatment pipeline has been shown to converge for regular clinical plans. Also for changing anatomies over the course of days and for changes during a single fraction the dose distribution converges to a clinically acceptable dose distribution. Currently the loop is fast enough, in the order minutes, for daily plan adaptation. We are working on speed optimization for the intra-fraction applications. The impact of the magnetic field has been shown to be an asymmetry in the penumbra, a reduced built updistance and most strikingly a dose increaseat tissue-air interfaces. It was shown that these effects can be mitigated by incorporating the magnetic field effects in the inverse optimization for IMRT. Also the impact on absolute, reference and relative dosimetry has been addressed. All exisiting dosimetry protocols can still be performed, albeit sometimes with adapted procedures and adapted detectors. In summary, the 1.5 T MRI linac is operational in a research setting and work on the clinical introduction is ongoing. The advent of on-line MRI directly from the treatment table enables true on-line adaptive radiotherapy.

Modification of the experimental setup of the FTIR spectrometer and thirty-meter optical cell for measurements of weak selective and nonselective absorptions

The improvement of the experimental setup based on a Fourier spectrometer Bruker IFS-125 and a 30-meter multipass optical cell is described. The improvement includes the cell equipment with a system of automated adjustment of the number of beam passes without cell depressurization and ensures the cell work at high temperatures.

Impurity and radiation defects in LiB3O5 crystals. The nature of centers in LiB3O5 crystals, which are responsible for coloration during the long-term operation of optical elements

An attempt is made to explain the causes of coloration of LiB3O5 crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB3O5 crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu2+ ions are found. Defect formation features in electron irradiated as-grown LiB3O5 crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen O– in the interstitial position, an O– hole center in the crystal structure, and the B2+ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB3O5 crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.

Tunable Terahertz Device Using Refractive Index Control

We measured the thermal dependencies of the refractive index and the absorption coefficient of high-resistivity silicon. We found that the refractive index varied slightly with temperature, and the absorption coefficient was very low and remained approximately constant as the temperature was changed. As a result, the conditions for terahertz propagation in silicon could be controlled by changing the refractive index without any absorption loss. As one application of this effect, we developed a terahertz time delay generator that can generate a terahertz time delay by changing the temperature of the medium through which the terahertz beam passes, without the need for any mechanical delay. We demonstrated generation of a terahertz time delay of approximately 6.6 ps.

Simulation of the energy loss of proton beams interacting with few layer graphene foils

SynopsisWe have simulated the passage of proton beams, having energies E < 10 keV, through graphene targets, considering the case of few layer foils. For this purpose and for comparison, we implement Monte Carlo and deterministic semi-classical approaches to describe the interaction of protons with carbon atoms in graphene structures. Our results show that the energy loss through a single layer graphene foil is smaller than recent ab initio calculations based on time dependent density functional theory (TD-DFT). Besides, for E > 6 keV the energy loss into a graphene target composed of n layers is n times the energy loss through a single layer graphene foil.

Transition from superhydrophilic to superhydrophobic state of laser textured stainless steel surface and its effect on corrosion resistance

This work investigates the evolution from superhydrophilic to superhydrophobic surface state on corrosion behaviour of SS316L produced by Nd:YAG nanosecond direct laser texturing (DLT). Results confirm perfect correlation among wettability and corrosion, hence superhydrophobic surface with a contact angle of 168±3.0° reflects in enhanced passivity, lower anodic dissolution and corrosion current reduction. Characterization of the corrosion attack by 3D microscopy reveals high sensitivity of superhydrophilic surfaces on corrosion propagation direction in regard to the laser beam passage (90°/0°). However, this trend completely diminishes with superhydrophobic development. Further, DLT also completely prohibits intergranular corrosion detected with the non-processed sample.

Channeling of low energy atomic particles in carbon nanotubes with heterojunctions

Low energy particle channeling through single-wall carbon nanotubes 245nm long with (20,0)/(10,10) heterojunction has been studied. As demonstrated the ion beam cross-section becomes half the area after beam passage through the heterojunction.

Angular distribution of beam electrons in a source with arc plasma emitter

Results on studying the angular characteristics of an electron beam, generated in a multi-aperture diode with an arc-discharge plasma emitter are reported. The main beam parameters were as follows: the electron energy up to 120 keV, the emission current up to 100 A, the pulse duration 0.1 - 0.3 ms, and the initial diameter ca. 8 cm. The beam was formed and transported to a metal target in an adiabatically converging magnetic field. The diagnostic technique based on an X-ray imaging of the profiles of individual beamlets passed through the pepperpot-like mask was developed and used to investigate an angular distribution of the beam electrons. The spatial resolution of the diagnostic was evaluated in a special test experiment and found to be not worse than 4 lp/cm at a 10 % contrast level. It was demonstrated that an angular distribution of the beam electrons fits well by the Gaussian function with the RMS width ∼ 0.067 rad. The data on the angular distribution measured with pepperpot diagnostic are in a good agreement with those obtained in the experiments on the beam passage through a magnetic mirror.

Hybrid CO2 laser waterjet heat (LWH) treatment of bindered boron nitride composites with hardness improvement

Boron nitride (BN) material is chemically and thermally stable which makes it desirable for high speed machining in demanding chemical and thermal environments. Although the hardness of BN material is well below that of single polycrystalline diamond (PCD), a laser waterjet heat (LWH) treatment process provides a new potential approach to achieve hardness values that are comparable to diamond hardness. This study investigates the hardness change of LWH-treated bindered cBN/TiN and cBN/AlN composites. Results indicate that measured hardness increase is dependent on the laser beam pass and the distance from the beam center.

New Variational Solutions for the Rolling of Flanged Sections in Universal Roll Passes

The variational principle of minimum total power and modern computational means are used to describe the deformation of metal in and to determine the power/force conditions for rolling rails and I-beams in universal beam passes. The results are engineering formulas for designing roll passes and calculating process parameters.

OpenPET: a novel open-type PET system for 3D dose verification in particle therapy

The OpenPET is the world’s first open-type 3D PET scanner for PET image-guided particle therapy such as in situ dose verification and direct tumour tracking. Even with a full-ring geometry, the OpenPET has an open gap between its two detector rings through which the treatment beam passes. Following the initial proposal of the dual-ring OpenPET (DROP), the single-ring OpenPET (SROP) was also proposed as a more efficient geometry than DROP in terms of manufacturing cost and sensitivity. A small SROP prototype was developed and feasibility of visualizing a 3D distribution of beam stopping positions inside a phantom was shown with the help of radioisotope particle beams, used as primary beams. Following these results, a full-size whole-body SROP prototype was developed.

Microbeam formation system

Equations for calculating the microbeam formation channel are derived. The channel consists of two coaxial diaphragms with radii r 1,2 and a target with a radius r T . With the given ion beam parameters, distance between the diaphragms L, beam radius on the target r T , and desired efficiency of beam passage through the diaphragms η0, the system of equations allows calculating the distance from the second diaphragm to the target L 1 and the radii of both diaphragms. Dependences of the diaphragm radii and the distance L 1on the efficiency η0 at a fixed target radius r T and of the efficiency η0 and the diaphragm radii r 1,2 on the distance L at a fixed distance L 1 are found. The effect of the deviations of the main channel and beam parameters from the optimum values on the microbeam formation efficiency is estimated. Tolerable values are determined for the diaphragm displacement and background magnetic field.

High frequency and multiphysical analysis of the multigap CH-resonators

Results of numerical electrodynamic modeling of multigap CH resonators with a variable period of structure if the balancing of the accelerating field on the center line of the beam passage is reached are presented in the article. Proton-beam dynamic analysis with the initial energy of 1.927 MeV and thermal modeling in a steady state regime are completed for the obtained models.

Ghost imaging with atoms.

Ghost imaging is a counter-intuitive phenomenon-first realized in quantum optics-that enables the image of a two-dimensional object (mask) to be reconstructed using the spatio-temporal properties of a beam of particles with which it never interacts. Typically, two beams of correlated photons are used: one passes through the mask to a single-pixel (bucket) detector while the spatial profile of the other is measured by a high-resolution (multi-pixel) detector. The second beam never interacts with the mask. Neither detector can reconstruct the mask independently, but temporal cross-correlation between the two beams can be used to recover a 'ghost' image. Here we report the realization of ghost imaging using massive particles instead of photons. In our experiment, the two beams are formed by correlated pairs of ultracold, metastable helium atoms, which originate from s-wave scattering of two colliding Bose-Einstein condensates. We use higher-order Kapitza-Dirac scattering to generate a large number of correlated atom pairs, enabling the creation of a clear ghost image with submillimetre resolution. Future extensions of our technique could lead to the realization of ghost interference, and enable tests of Einstein-Podolsky-Rosen entanglement and Bell's inequalities with atoms.